For a broadband transformer the “rule of thumb” is that the reactance of the low impedance winding should be 4x the impedance ?at the lowest frequency of operation. So for a 50 to 450 ohm transformer operating down to 4 MHz. you need a reactance of 200 ohms at this frequency. ?So you calculate the inductance required and the number of turns. ?If 5 turns are required then you need 15 for the other winding.?
Roger Need